Neuronal apoptosis is a common pathological feature in neurological disorders of diverse etiology. Viral encephalitis, an exemplary disease associated with neuronal apoptosis, remains a significant cause of morbidity and mortality due to severely limited diagnostic and treatment options. The primary goal of the proposed research is to utilize in vivo, ex vivo, and in vitro models of reovirus infection to characterize signaling pathways activated during neuronal viral infection and, ultimately, to identify novel therapeutic targets for neuroprotection. Fas death receptor signaling and c-Jun N-terminal Kinase (JNK) activation are known to contribute to reovirus-induced neuronal apoptosis. These seemingly isolated findings are consolidated into a broader model, described in this proposal. As discovered in various non-viral models of apoptosis, Fas signaling originating at the cell membrane may initiate intracellular JNK activation by proceeding through the Fas-Daxx-ASK1-Sek1-JNK apoptotic pathway. I hypothesize that Daxx is an especially important mediator of apoptosis in the context of viral infection because its expression is controlled by the host anti-viral immune response. In Aim 1, models of dominant-negative Daxx overexpression (in vivo and in vitro) and siRNA- mediated Daxx knockdown (in vitro only) will be utilized to determine the relative importance of Daxx in reovirus-induced apoptosis and neuropathogenesis. Aim 2 will employ immunofluorescence imaging and Western blotting techniques to assess the binding interactions and signaling roles of Daxx following reovirus infection. Finally, Aim 3 will address the possibility that Daxx expression is regulated by interferon (IFN) released by the virally infected host. Overall, I hypothesize that IFN signaling and consequential Daxx gene expression leaves virally infected neurons vulnerable to apoptosis. The proposed studies will probe the interfaces between viral infection, immunity, and cellular/tissue/host death to deepen our understanding of the viral-host interaction and neuronal apoptotic signaling. Furthermore, these studies will potentially build the theoretic basis for the eventual development of neuroprotective pharmaceuticals. PUBLIC HEALTH RELEVANCE: Neuron death may occur in patients suffering from some types of brain disease. We expect that the protein, Daxx, may play a role in causing death of virus-infected neurons. Understanding how Daxx may contribute to anti-viral immunity and neuron death may lead to the development of new therapies for devastating brain diseases, such as encephalitis.